Fish – Cooking thawed fish when it says cook from frozen

As long as you complete the salmon's cooking in the sauce, it's fine. If you're not sure when the salmon's done by your method, I'd suggest completing its cooking in the microwave as directed by the package and then adding it to the pasta and sauce just before preparing to serve the dish.

There's always the delight of botulism, which thrives in the anaerobic environment provided by vacuum packing. Listeria and vibrio bacteria can grow in an anaerobic environment, and are potential food safety risks present in fish.

With this in mind, I would not expect vacuum packing to extend the life of a fish much. It will reduce freezer burn though!